1. Field of the Invention
The present invention relates to a transducer plate for piezoelectric transducers, particularly for transducers of the type for use in receivers in telephone systems, and which consists of electrically conductive material whose two sides carry piezoceramic and electrodes, the piezoceramic being applied by way of an electrically-insulating adhesive layer, and to apparatus for manufacturing such a transducer plate.
2. Description of the Prior Art
Transducer plates for piezoelectric transducers, particularly for receivers in telephone systems, are usually held clamped in the region of their edges between bearing members and are connected to a piezoceramic which is provided with electrodes at both sides, whereby the electrical speed to the electrode of the piezoceramic can be produced via ribbon connectors or the like.
Such transducer plates are known from various publications.
The German published application No. 31 07 344 and the German published application No. 31 07 293, both incorporated herein by this reference, disclose a transducer plate held clamp in its edge region by bearing members.
The connection between a transducer plate consisting of electrically-conductive material and the piezoceramic provided with electrodes on both sides can occur with an electrically-insulating adhesive layer under the influence of heat and pressure. It is known from the German published application No. 28 20 403, fully incorporated herein by this reference, to thereby contact the inner electrode of the piezoceramic at the adhesive side by way of a ribbon connector which is somewhat thinner than the adhesive layer and is placed on the adhesive layer before the application of the piezoceramic.
Piezoelectric transducers belong to the group of reversible transducers, i.e. they can be electrically excited and emit sound or vice-versa. These transducers can thus be versatility employed. They can therefore be utilized as transmitters, earphones or as acoustic signal generators in telephone systems. Depending upon its utilization, the transducer must be specifically matched to the requirements of, for example, an earphone (receiver), i.e. an amplifier must be provided under given conditions or the resonator spaces and the sound conducting channel must be matched to the respective use.
A transducer capacitance of about 200 nF is required given the use of piezoelectric transducers as telephone receivers in order to achieved the necessary voltage response, since the telephone receiver is therewith matched to the telephone. Two solutions have been disclosed for the realization thereof. The one solution consists of the use of a very thin ceramic having a mean dielectric constant of .epsilon.=1500, while the other solution consists of the use of a mean ceramic thickness of about 100 .mu.m with a higher dielectric constant of .epsilon.=4000. The former solution can lead to problems in the automatic bonding of the thin ceramic. The second solution requires a high dielectric constant, which results in a higher temperature dependency of the ceramic.
In order to keep the temperature dependency of the transducer negligibly small, without requiring an all too thin ceramic layer, it has already been proposed in-house of the assignee of the present invention, that a respective piezoceramic be provided with electrodes on both sides and be applied to the transducer plate and that the two piezoceramics be electrically connected in parallel.